This invention relates to a method of producing hydrogen. In more detail, the invention relates to the thermochemical decomposition of water to produce hydrogen.
An assured long-term supply of inexpensive energy is essential for maintenance and growth of a modern industrial society. It has been suggested -- see, for example, pages 13-21 of Scientific American for January 1973 -- that hydrogen is an excellent choice as a general fuel or energy carrier because it is nonpolluting and can be produced from energy sources other than fossil fuel. Hydrogen can be burned to develop thermal energy or used in a fuel cell to develop electrical energy. However, if hydrogen is to become the fuel of the future, new procedures for producing it economically in large quantities will have to be developed.
Presently hydrogen is produced by cracking natural hydrocarbons, by reacting coal with water or by the electrolysis of water. It is only by decomposing water using energy obtained from a nonfossil-fueled source such as nuclear or solar energy that depletion of fossil fuel reserves can be avoided.
To electrolyze water, primary energy in the form of heat -- nuclear, geothermal or solar -- or hydrostatic head must be converted into electrical energy. Such processes are inherently inefficient and, in addition, require a large capital investment which adversely affects the cost of the final product. Apart from cost, there is the problem of the availability of electrical power. To replace the thermal equivalent of all the fossil fuel currently consumed in the United States by electrolytic hydrogen would require at least a fifteenfold increase in the present electrical generating capacity and, if only nuclear powered capacity is admitted, at least 150-fold increase. Clearly, an alternate to processes currently in commercial use must be developed if hydrogen is to become the energy carrier of the future.
A thermochemical process not requiring conversion of primary heat into electricity would be ideally suited for the purpose provided the temperature of operation were sufficiently low that available sources of heat could be used. It has been shown that a single-stage thermochemical process for the production of hydrogen is not possible below 2227.degree. K. Several of these processes are described in De Beni and Marchetti, Proceedings of the Symposium on Nonfossil Chemical Fuels, Boston Mass., April 10-14, 1972, pages 100-133. All of these processes require temperatures higher than those available from presently operating nuclear reactors and geothermal sources. A thermochemical process utilizing lower temperatures was disclosed in U.S. Pat. No 3,929,980 and assigned to the common assignee. However, the reaction ratios in that process are slow and the process disclosed therein is not economically feasible.